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For 50 years or so, scientists have generally been on the same page about what matter is
made of.
It’s a collection of particles that includes common things, like electrons, and also some
rare ones, like strange quarks.
But according to a paper published last week in the journal Physical Review Letters, maybe
there’s more to it than that.
Maybe a signal coming from a cluster of dead stars could be caused by a particle beyond
our standard model of the universe.
The “dead stars” here are neutron stars.
They form when stars a lot more massive than our Sun run out of fuel, and their cores collapse.
Neutron stars pack the mass of the entire Sun into a sphere around 20 kilometers wide,
and they’re home to some of the strongest magnetic fields we know of.
But they might also have a surprise inside: a bunch of currently-hypothetical particles
called axions.
The idea of axions showed up in the 1970s, when theoretical physicists were trying to
explain a weird property about neutrons.
Without going too far into the weeds, it was basically about how electric charge is distributed
inside these particles, and it’s part of something called “the strong CP problem.”
But the bigger point is, these researchers proposed you could solve the problem by tweaking
our model of the universe to include a new field, and also a new particle called an axion.
So, where do neutron stars come in?
Well, given that these things are full of neutrons, they might be a good place to start
looking for axions.
Supposedly, axions would form when neutrons smashed into one another.
Then, as they escaped into space and interacted with the star’s magnetic field, they’d
change into particles of X-ray light we could detect.
So, if astronomers ever saw more X-ray radiation around a neutron star than expected, that
might indicate axions are really out there.
And that’s actually what scientists reported last November, while they were studying two
neutron stars in a cluster nicknamed the Magnificent 7.
They’d caught the stars releasing more X-rays than anticipated.
And in this latest paper, a group argues that axions could be to blame.
After all, if there was some other object out there making the X-rays, it would have
shown up in telescope surveys.
That said, this is far from a smoking gun.
Like, our estimates of what these stars should act like could also be wrong!
To learn more, the team proposed that someone could try and find an excessive amount of
X-rays around another kind of stellar remnant called white dwarfs.
They don’t emit nearly as much X-ray radiation as neutron stars.
So if any of their neutrons are busy making axions, it would be more obvious.
Still, it may turn out that this signal doesn’t lead to the discovery of a new particle.
But it will help us put together a more accurate model of how these dead stars work.
Next, in a paper published Monday in Nature Astronomy, researchers proposed that we might
need to change our story about how Saturn got so askew.
Because it seems we’ve been underestimating a key character: Saturn’s moon Titan.
So, lots of planets in our solar system are tilted relative to the plane they go around
the Sun, including Earth.
Astronomers call it obliquity.
Like, Earth’s obliquity is around 23.5 degrees.
It’s what gives us seasons.
Coincidentally, Saturn’s tilt is pretty similar, at 26.7 degrees.
But on Saturn, that’s a bigger deal.
It’s generally thought that gas giants don’t form with a serious tilt, partly because it’s
harder to knock them over.
So, if we see a tilt, that’s a sign that something big happened in the past.
With Saturn, the hypothesis is that the planet fell over more than four billion years ago,
while the gas giants were migrating from where they formed, to where they are today.
During that period, Saturn settled into a relationship with Neptune.
Each time Neptune passed by, it gravitationally tugged on Saturn.
And as this repeated over the years, it became enough to destabilize Saturn and tip the planet
over.
Except, this paper calls that into question, based on new observations of Saturn’s largest
moon, Titan.
See, as Titan circles Saturn, its gravity also pulls on the planet.
It’s nowhere near enough to have knocked Saturn over.
But it is enough to have messed with that process — especially because Titan’s pull
isn’t constant over huge lengths of time.
That’s because the moon is moving away from its planet.
In fact, just last year, we learned that it’s migrating away 100 times faster than predicted!
So, Titan’s influence on Saturn has been shifting more than we thought.
Based on that discovery, astronomers ran calculations to figure out how this would change Saturn’s
obliquity.
And the answer is… a lot!
The team concluded that Saturn’s tilt couldn’t have drastically changed four billion years
ago because Titan’s ever-changing pull would have kept Saturn from settling into the relationship
with Neptune that knocked it over.
At least, until about one billion years ago.
It’s not clear what’s special about that time, but the team’s model suggests it’s
when Saturn’s tilt finally ramped up — three billion years later than we thought.
If further research confirms this, astronomers won’t have just learned something about
Saturn.
They’ll have learned concepts that could apply to a range of gas giants, including
many beyond our solar system.
And that’s one of the wonderful things about astronomy.
Sometimes, studying just one planet, or one
cluster of neutron stars, can open doors to
understanding the whole universe.
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